Amplifier for floating voltage source

A differential amplifier is arranged to amplify faithfully the voltage produced by an ungrounded voltage source to provide the amplified result as a voltage in relation to a reference (ground) voltage. Errors resulting from leakage resistances between the ungrounded voltage source and ground are avoided by providing an inverting amplifier responsive to the output voltage, which draws, through a resistance, a current from a terminal of the voltage source which is proportional to the output voltage of the differential amplifier. This causes a shift of the potential of the voltage source in the direction towards the reference voltage. Optimum results are obtained when the shift is such that the variations in the voltage source being observed are caused to become balanced in relation to the reference potential. As applied to a thermocouple voltage source located in a furnace or engine, the circuit can be made to become balanced when there is a small residual current through the thermocouple, so that a fracture of the thermocouple will produce an immediately recognizable response.